This invention relates to a silicone rubber adhesive composition which can be simply and briefly molded by injection molding and exhibits good adhesion enough to allow for primerless molding and hence, integral molding with a thermoplastic resin. It also relates to an integrally molded article of a silicone rubber adhesive composition bonded to a thermoplastic resin.
Nowadays silicone rubber, due to its excellent characteristics, finds widespread use in a variety of fields including electric, electronic, automotive and building fields. The demands for the silicone rubber in these fields include workability, seal and insulation during assembly. In some applications where the adhesion of silicone rubber to resins is necessary, adhesion is achieved by way of primers. The process requires the step of applying primer and is thus cumbersome. One solution is a self-adhesive type silicone rubber obtained by adding an adhesive to a silicone rubber composition. The self-adhesive type silicone rubber eliminates the application step, shortens the operating time, reduces the cost, and improves the efficiency of operation. It is effective in manufacturing integrally molded articles with resins.
In connection with the primerless molding of addition type heat-curable silicone rubber, a number of reports have been made for bonding silicone rubber to organic resins. In one exemplary attempt, self-adhesive type silicone rubber material is cured on resins. A number of proposals have been made relating to specific adhesive components for use in the self-adhesive type silicone rubber. Also, JP-B 2-34311 corresponding to U.S. Pat. Nos. 4,582,762, 4,686,124, 4,814,231 and U.S. Pat. No. 4,834,721 discloses to add an organopolysiloxane containing at least 30 mol % of hydrogen atoms directly bonded to silicon atoms to an organic resin whereby the resin is bondable to an addition curing type silicone rubber. JP-B 63-45292 discloses the integration of silicone rubber to organic resin by physical engagement. JP-A 63-183843 corresponding to EP 0276790B discloses the integral adhesion of silicone rubber to an olefin resin having grafted thereto a compound having an aliphatic unsaturated group and a silicon atom-bonded hydrolyzable group. JP-A 9-165516 corresponding to U.S. Pat. No. 5,879,809 and JP-A 9-165517 corresponding to U.S. Pat. No. 5,989,704 of Shin-Etsu Chemical Co., Ltd. propose a process in which a thermoplastic resin having added thereto a compound having unsaturated groups and hydrogen atoms directly bonded to silicon atoms is adhesively joined and integrated with silicone rubber as well as an integrally molded article in which a thermoplastic resin having blended therein a thermoplastic oligomer containing aliphatic unsaturated groups is integrally molded with an oil-bleeding silicone rubber.
However, heat curable silicone rubber of the addition type fails to achieve within brief molding a sufficient bond to general thermoplastic resins such as ABS, PPO, PPS, PC, PE, PP, PBT, acrylic, PA and aromatic PA. To acquire a bonding ability, the resins must be modified as suggested in the above patents. Modification of resins requires extra steps and an increased cost, and the modified resins sometimes become susceptible to quality alteration. Even if a bond is established, without resin modification, in forming an integrated silicone rubber/resin article in a mold, there arises a problem that the molded article sticks to the mold. In particular, none of polyamide resins fully satisfy the requirements. It remains of interest to develop an integrally molded article of thermoplastic resin and silicone rubber which when formed in a mold, does not stick to the mold and establishes a firm bond between the thermoplastic resin and the silicone rubber.
An object of the invention is to provide a silicone rubber adhesive composition which can be firmly integrated with thermoplastic resins, as well as an integrally molded article thereof with a thermoplastic resin.
It has been found that a silicone rubber adhesive composition comprising a silicone rubber component, an adhesive agent, and a compound having at least one ester group in a molecule, preferably further containing at least one aliphatic unsaturated group is firmly bondable to thermoplastic resins. When this silicone rubber adhesive composition is molded and joined with a thermoplastic resin, there is obtained an integrally molded article in which the silicone rubber is firmly bonded to the thermoplastic resin. Even under brief curing conditions using an injection molding technique, the silicone rubber adhesive composition develops a sufficient bonding force to the thermoplastic resin. The integrally molded article of silicone rubber/thermoplastic resin can be released from the mold in a practically acceptable way. The silicone rubber adhesive composition is effective even to highly crystalline polyamide resins such as nylon 66 and aromatic polyamides.
The invention provides a silicone rubber adhesive composition comprising
(A) 100 parts by weight of a heat curable organopolysiloxane composition,
(B) 1 to 100 parts by weight of reinforcing silica fines,
(C) 0.1 to 50 parts by weight of an adhesive agent, and
(D) 0.05 to 20 parts by weight of a compound having at least one ester group in a molecule.
Also contemplated herein is an integrally molded article comprising the cured silicone rubber adhesive composition (i.e., silicone rubber) and a thermoplastic resin.